TECHNICAL FIELD

[0001] The present disclosure relates to a composition comprising a partially fluorinated amorphous polymer in an ionic liquid. Methods of making an article using the composition are disclosed herein.

SUMMARY

[0002] Due to their elasticity and inertness to chemical reactivity, heat, or both, fluoropolymeric elastomers are useful in making articles such as seals, gaskets, o-rings, and hoses. Many of the copolymers used to make fluoropolymeric elastomers have relatively high viscosities in comparison to non-fluorinated materials used to make elastomers (e.g., silicones for silicone elastomers). Typically, solvents such as acetone, 2-butanone, 4-methyl-2 -pentanone, cyclohexanone, methyl formate, ethyl formate, methyl acetate, ethyl acetate, n-butyl acetate, tertbutyl acetate, or dimethyl carbonate are used to reduce the viscosity of the fluoropolymeric compositions. However, these solvents are flammable, and therefore explosion-protected measures are needed for manufacturing processes and equipment.

[0003] Thus, there is a desire to reduce the cost of fluoropolymeric elastomeric articles. Such cost reductions can include using a partially fluorinated polymer, which is typically cheaper than its perfluororinated counterpart; using a non-flammable, more environmentally friendly solvent; and optionally making products in a continuous fashion versus a batch-type process.

[0004] In one aspect, a curable composition is disclosed. The curable fluoropolymer composition comprising:

(a) a partially fluorinated amorphous polymer comprising at least one of an iodine, a bromine, and a nitrile cure site;

(b) a photoinitiator;

(c) a crosslinking agent; and

(d) an ionic liquid.

[0005] In one aspect, a method of making a gasket is disclosed. The method comprising (i) applying a coatable composition comprising a partially fluorinated amorphous polymer comprising at least one of an iodine, a bromine, and a nitrile cure site; a photoinitiator; a crosslinking agent; and an ionic liquid; and (ii) curing the coatable composition. [0006] The above summary is not intended to describe each embodiment. The details of one or more embodiments of the invention are also set forth in the description below. Other features, objects, and advantages will be apparent from the description and from the claims.

DETAILED DESCRIPTION

[0007] As used herein, the term

“and/or” is used to indicate one or both stated cases may occur, for example A and/or B includes, (A and B) and (A or B);

“backbone” refers to the main continuous chain of the polymer;

“crosslink” refers to connecting two pre-formed polymer chains using chemical bonds or chemical groups;

“cure site” refers to functional groups, which may participate in crosslinking;

“interpolymerized” refers to monomers that are polymerized together to form a polymer backbone;

“monomer” is a molecule which can undergo polymerization which then form part of the essential structure of a polymer;

“perfluorinated” means a group or a compound derived from a hydrocarbon wherein all hydrogen atoms have been replaced by fluorine atoms. A perfluorinated compound may however still contain atoms other than fluorine and carbon atoms, like oxygen atoms, chlorine atoms, bromine atoms and iodine atoms; and

“polymer” refers to a macrostructure having a number average molecular weight (Mn) of at least 10,000, 30,000, 50,000, 100,000, 200,000, 500,000, or even at least 1,000,000 dalton and not such a high molecular weight as to cause premature gelling of the polymer.

[0008] Also herein, recitation of ranges by endpoints includes all numbers subsumed within that range (e.g., 1 to 10 includes 1.4, 1.9, 2.33, 5.75, 9.98, etc.).

[0009] Also herein, recitation of “at least one” includes all numbers of one and greater (e.g., at least 2, at least 4, at least 6, at least 8, at least 10, at least 25, at least 50, at least 100, etc.).

[0010] Disclosed herein is a curable fluoropolymer composition. This curable fluoropolymer composition comprises a partially fluorinated amorphous polymer in an ionic liquid. These curable fluoropolymer compositions can be cured via actinic radiation. The compounds curable fluoropolymer compositions of the present disclosure have good environmental properties as well as having good performance attributes, such as non-flammability, and ability to cure.

[0011] Amorphous Fluoropolymer

[0012] The fluoropolymers of the present disclosure are amorphous, meaning that there is an absence of long-range order (i.e., in long-range order the arrangement and orientation of the macromolecules beyond their nearest neighbors is understood). The amorphous polymer has no detectable crystalline character by DSC (differential scanning calorimetry). If studied under DSC, the fluoropolymer would have no melting point or melt transitions with an enthalpy more than 0.002, 0.01, 0.1, or even 1 Joule/g from the second heat of a heat/cool/heat cycle, when tested using a DSC thermogram with a first heat cycle starting at -85°C and ramped at 10 °C/min to 350°C, cooling to -85°C at a rate of 10°C/min and a second heat cycle starting from -85°C and ramped at 10 °C/min to 350°C.

[0013] In one embodiment, the amorphous fluoropolymers of the present disclosure decompose above a temperature of 350, 325, 300, or even 275°C.

[0014] The amorphous fluoropolymers of the present disclosure are partially fluorinated. A partially fluorinated amorphous polymer comprises both C-F and C-H bonds along the carbon backbone of the polymer chain.

[0015] In one embodiment, the amorphous fluoropolymer of the present disclosure comprises at least 30, 50, 60, 66, 68, 70, or even 71% by weight of fluorine, and no more than 72, or even 73% by weight of fluorine (based on the total weight of the amorphous fluoropolymer).

[0016] In one embodiment, the amorphous fluoropolymer is derived from at least one hydrogencontaining monomer and at least one fluorine -containing monomer. In one embodiment, the amorphous fluoropolymer is derived from a monomer comprising both an olefinic hydrogen and an olefinic fluorine, such as vinylidene fluoride. Hydrogen containing monomers include those known in the art. The hydrogen-containing monomers may or may not contain fluorine atoms. Exemplary hydrogen-containing monomers include: vinylidene fluoride, pentafluoropropylene (e.g., 2-hydropentafluoropropylene), vinyl fluoride, trifluoroethylene, propylene, ethylene, isobutylene, and combinations thereof. Fluorine-containing monomers include those known in the art. Exemplary fluorine-containing monomers include: hexafluoropropene, tetrafluoroethylene, chlorotrifluoroethylene, perfluoro(alkylvinyl ether) (such as perfluoromethyl vinyl ether, perfluoropropyl vinyl ether, CF2=CFOCF2CF2CF2OCF3, CF2=CFOCF2OCF2CF2CF3, CF2=CFOCF2OCF2CF3, and CF2=CFOCF2OCF3), and combinations thereof.

[0017] In one embodiment, the amorphous fluoropolymer comprises interpolymerized units derived from vinylidene fluoride (VDF). In one embodiment, the amorphous fluoropolymer is derived from 25-75 wt % VDF or even 35-70 wt % VDF.

[0018] In one embodiment, the amorphous fluoropolymer comprises interpolymerized units derived from (i) hexafluoropropylene (HFP), tetrafluoroethylene (TFE), and vinylidene fluoride (VDF); (ii) HFP and VDF, (iii) VDF and perfluoromethyl vinyl ether (PMVE), (iv) VDF, TFE, and PMVE, (v) VDF, TFE, and propylene, (vi) ethylene, TFE, and PMVE, (vii) TFE, VDF, PMVE, and ethylene, and (viii) TFE, VDF, and CF2=CFO(CF2)3OCF3. [0019] In one embodiment, the amorphous fluoropolymer comprises interpolymerized units derived from at least 25, 30, 40, 45, 50, or even 60 wt% and at most 65, 70, or even 75 wt% VDF; and at least 25, 30 or even 35 wt% and at most 50, 60, or even 70 wt% HFP. In one embodiment, the amorphous fluoropolymer comprises interpolymerized units derived from at least 45, 50, 55, or even 60 wt% and at most 65, 70, or even 75 wt% VDF; at least 10, 15, or even 20 wt% and at most 30, 35, 40, or even 45 wt% HFP; and at least 3, 5, or even 7 wt% and at most 10 or even 15 wt% TFE. In one embodiment, the amorphous fluoropolymer comprises interpolymerized units derived from at least 25, 30, or even 35 wt% and at most 40, 45, 50, 55, or even 65 wt% VDF; at least 15, 20, 25, or even 30 wt% and at most 35, 40, or even 45 wt% HFP; and at least 1, 5, 10 15, 20, or even 30 wt% and at most 30, 35, or even 40 wt% TFE. In one embodiment, the amorphous fluoropolymer comprises interpolymerized units derived from at least 30, 35, 40, or even 45 wt% and at most 55, 60, or even 65 wt% VDF; at least 25, 30, or even 35 wt% and at most 40, 45, 50, 55, 60, or even 65 wt% PMVE; and at least 3, 5, or even 7 wt% and at most 10, 15, or even 20 wt% TFE. In one embodiment, the amorphous fluoropolymer comprises interpolymerized units derived from at least 30, 35, 40, or even 45 wt% and at most 55, 60, or even 65 wt% VDF; at least 10, 15, 20, 25, or even 35 wt% and at most 40, 45, 50, 55, or even 60 wt% PMVE; and at least 10 15, or even 20 wt% and at most 25, 30, or even 35 wt% TFE. In one embodiment, the amorphous fluoropolymer comprises interpolymerized units derived from at least 5, 10, or even 15 wt% and at most 20, 25, or even 30 wt% VDF; at least 5, 10, or even 15 wt% and at most 20, 25, or even 30 wt% propylene; and at least 50, 55, 60, or even 65 wt% and at most 70, 75, 80, or even 85 wt% TFE. In one embodiment, the amorphous fluoropolymer comprises interpolymerized units derived from a perfluorinated ether monomer of the formula CF2=CF(CF2)pO(RfiO) _n (Rf O) _m Rf where Rn and Rf2 are different linear or branched perfluoroalkylene groups containing 2, 3, 4, 5, or 6 carbon atoms; m and n are independently 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10, p is 0 or 1, and Rfis a perfluoroalkyl group of 1, 2, 3, 4, 5, or 6 carbon atoms. Such perfluorinated ether compounds are known in the art and include for example, perfluorinated alkyl vinyl ether such as perfluorinated methyl vinyl ether (PMVE), perfluorinated alkyl allyl ether such as perfluorinated methyl allyl ether, and perfluorinated alkoxy vinyl ether and perfluorinated alkoxy allyl ether.

[0020] The amorphous fluoropolymer of the present disclosure contains cure sites which facilitate cross-linking of the fluoropolymer. These cure sites comprise at least one of I, Br, and CN. The fluoropolymer may be polymerized in the presence of a chain transfer agent and/or cure site monomers to introduce cure sites into the fluoropolymer. Such cure site monomers and chain transfer agents are known in the art. Exemplary chain transfer agents include: an iodo-chain transfer agent, a bromo-chain transfer agent, or a chloro-chain transfer agent. For example, suitable iodo-chain transfer agent in the polymerization include the formula of RI _X , where (i) R is a perfluoroalkyl or chloroperfluoroalkyl group having 3 to 12 carbon atoms; and (ii) x = 1 or 2. The iodo-chain transfer agent may be a perfluorinated iodo-compound. Exemplary iodo-perfluoro- compounds include 1,3 -diiodoperfluoropropane, 1,4-diiodoperfluorobutane, 1, 6- diiodoperfluorohexane, 1,8-diiodoperfluorooctane, 1,10-diiodoperfluorodecane, 1,12- diiodoperfluorododecane, 2-iodo-l,2-dichloro-l, 1,2-trifluoroethane, 4-iodo- 1,2,4- trichloroperfluorobutan, and mixtures thereof. In some embodiments, the iodo-chain transfer agent is of the formula I(CF2) _n -O-Rf-(CF2) _m I, wherein n is 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10, m is is 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 and Rf is a partially fluorinated or perfluorinated alkylene segment, which can be linear or branched and optionally comprises at least one catenated ether linkage. Exemplary compounds include: I-CF2-CF2-O-CF2-CF2-I, I-CF(CF ₃ )-CF2-O-CF2-CF ₂ -I, I-CF ₂ -CF ₂ -O-CF(CF ₃ )- CF2-O-CF2-CF2-I, I-(CF(CF ₃ )-CF2-O)2-CF ₂ -CF ₂ -I, I-CF ₂ -CF ₂ -O-(CF ₂ ) ₂ -O-CF ₂ -CF ₂ -I, I-CF2-CF2- O-(CF ₂ ) ₃ -O-CF ₂ -CF ₂ -I, and I-CF ₂ -CF ₂ -O-(CF ₂ ) ₄ -O-CF ₂ -CF ₂ -I, I-CF ₂ -CF ₂ -CF ₂ -O-CF ₂ -CF ₂ -I, and I- CF2-CF2-CF2-O-CF(CF ₃ )-CF2-O-CF2-CF2-I, In some embodiments, the bromine is derived from a brominated chain transfer agent of the formula: RBr _x , where (i) R is a perfluoroalkyl or chloroperfluoroalkyl group having 3 to 12 carbon atoms; and (ii) x = 1 or 2. The chain transfer agent may be a perfluorinated bromo-compound.

[0021] Cure site monomers, if used, comprise at least one of a bromine, iodine, and/or nitrile cure moiety.

[0022] In one embodiment, the cure site monomers may be of the formula: CX2=CX(Z), wherein: (i) X each is independently H or F; and (ii) Z is I, Br, R/-U wherein U=I or Br and R/=a perfluorinated or partially perfluorinated alkylene group optionally containing ether linkages. In addition, non-fluorinated bromo-or iodo-olefins, e.g., vinyl iodide and allyl iodide, can be used. Exemplary cure site monomers include: CH2=CHI, CF2=CHI, CF ₂ =CFI, CH2=CHCH2l, CF ₂ =CFCF ₂ I, ICF2CF2CF2CF2I, CH ₂ =CHCF ₂ CF ₂ I, CF ₂ =CFCH ₂ CH ₂ I, CF ₂ =CFCF ₂ CF ₂ I, CH ₂ =CH(CF ₂ ) ₆ CH ₂ CH ₂ I, CF ₂ =CFOCF ₂ CF ₂ I, CF ₂ =CFOCF ₂ CF ₂ CF ₂ I, CF ₂ =CFOCF ₂ CF ₂ CH ₂ I, CF2=CFCF ₂ OCH2CH ₂ I, CF2=CFO(CF ₂ ) ₃ -OCF2CF ₂ I, CH ₂ =CHBr, CF ₂ =CHBr, CF ₂ =CFBr, CH ₂ =CHCH ₂ Br, CF ₂ =CFCF ₂ Br, CH2=CHCF ₂ CF ₂ Br, CF2=CFOCF ₂ CF ₂ Br, CF ₂ =CFC1, 1-CF ₂ - CF2CF2-O-CFCF2, 1-CF ₂ -CF2CF2-O-CF ₂ CF=CF2, 1-CF2-CF ₂ -O-CF2-CF=CF ₂ , I-CF(CF ₃ )-CF ₂ -O- CF=CF ₂ , 1-CF(CF ₃ )-CF2-O-CF ₂ -CF=CF ₂ , 1-CF ₂ -CF2-O-CF(CF ₃ )-CF2-O-CF=CF ₂ , 1-CF2-CF2-O- CF(CF ₃ )-CF2-O-CF2-CF=CF2, 1-CF2-CF2-(O-(CF(CF ₃ )-CF ₂ )2-O-CF=CF2, I-CF ₂ -CF ₂ -(O-(CF(CF ₃ )- CF2)2-O-CF2-CF=CF2, Br-CF2-CF2-O-CF2-CF=CF ₂ , Br-CF(CF ₃ )-CF ₂ -O-CF=CF ₂ , I-CF ₂ -CF ₂ -CF ₂ - O-CF(CF ₃ )-CF2-O-CF=CF2, I-CF2-CF2-CF2-O-CF(CF ₃ )-CF2-O-CF2-CF=CF ₂ , I-CF ₂ -CF ₂ -CF ₂ -(O- (CF(CF ₃ )-CF2)2-O-CF=CF2, I-CF2-CF2-CF2-O-(CF(CF ₃ )-CF2-O)2-CF2-CF=CF ₂ , Br-CF ₂ -CF ₂ -CF ₂ - O-CF=CF ₂ , Br-CF2-CF2-CF2-O-CF2-CF=CF ₂ , 1-CF ₂ -CF2-O-(CF2)2-O-CF=CF ₂ , 1-CF2-CF2-O- (CF ₂ ) ₃ -O-CF=CF2, 1-CF2-CF2-O-(CF ₂ ) ₄ -O-CF=CF2, 1-CF2-CF2-O-(CF ₂ )2-O-CF2-CF=CF2, 1-CF2- CF ₂ -O-(CF ₂ ) ₃ -O-CF ₂ -CF=CF ₂ , I-CF ₂ -CF ₂ -O-(CF ₂ ) ₂ -O-CF(CF ₃ )CF ₂ -O-CF ₂ =CF ₂ , I-CF ₂ -CF ₂ -O- (CF ₂ ) ₂ -O-CF(CF ₃ )CF ₂ -O-CF ₂ -CF ₂ =CF ₂ , Br-CF ₂ -CF ₂ -O-(CF ₂ ) ₂ -O-CF=CF ₂ , Br-CF ₂ -CF ₂ -O-(CF ₂ ) ₃ - O-CF=CF ₂ , Br-CF ₂ -CF ₂ -O-(CF ₂ ) ₄ -O-CF=CF ₂ , and Br-CF ₂ -CF ₂ -O-(CF ₂ ) ₂ -O-CF ₂ -CF=CF ₂

[0023] In another embodiment, the cure site monomers comprise nitrile-containing cure moieties. Useful nitrile-containing cure site monomers include nitrile-containing fluorinated olefins and nitrile-containing fluorinated vinyl ethers, such as: perfluoro(8-cyano-5-methyl-3,6-dioxa-l- octene); CF ₂ =CF-O-(CF ₂ ) _n -CN where n = 2-12, preferably 2, 3, 4, 5, or 6. Examples of a nitrile- containing cure site monomer include CF ₂ =CF-O-[CF ₂ -CFCF ₃ -O] _n -CF ₂ -CF(CF ₃ )-CN; where n is 0, 1, 2,3, or 4, preferably 0, 1, or 2; CF ₂ =CF-[OCF ₂ CF(CF ₃ )] _x -O-(CF ₂ ) _n -CN; where x is 1 or 2, and n is 1, 2, 3, or 4; and CF ₂ =CF-O-(CF ₂ ) _n -O-CF(CF ₃ )CN where n is 2, 3, or 4. Exemplary nitrile- containing cure site monomers include: CF ₂ =CFO(CF ₂ )5CN, CF ₂ =CFOCF ₂ CF(CF ₃ )OCF ₂ CF ₂ CN, CF ₂ =CFOCF ₂ CF(CF ₃ )OCF ₂ CF(CF ₃ )CN, CF ₂ =CFOCF ₂ CF ₂ CF ₂ OCF(CF ₃ )CN, CF ₂ =CFOCF ₂ CF(CF ₃ )OCF ₂ CF ₂ CN; and combinations thereof.

[0024] The amorphous fluoropolymer composition of the present disclose comprises iodine, bromine, and/or nitrile cure sites, which are subsequently used to crosslink the amorphous fluoropolymer. In one embodiment, the amorphous fluoropolymer composition of the present disclosure comprises at least 0.1, 0.5, 1, 2, or even 2.5 wt% of iodine, bromine, and/or nitrile groups versus the total weight of the amorphous fluoropolymer. In one embodiment, the amorphous fluoropolymer of the present disclosure comprises no more than 3, 5, or even 10 wt% of iodine, bromine, and/or nitrile groups versus the total weight of the amorphous fluoropolymer. [0025] In one embodiment, the amorphous fluoropolymer comprising cure sites is blended with a second amorphous fluoropolymer, which may or may not comprise bromine, iodine, and/or nitrile cure sites.

[0026] Photoinitiator

[0027] The curable compositions of the present disclosure comprise a photoinitiator. In one embodiment, the initiator is a photoinitiator, which when exposed to actinic radiation, causes the composition to at least partially cure. As used herein, partially cured refers to a state that the crosslinking degree in the fluoropolymer is higher than that in an uncrosslinked fluoropolymer, which can be observed by an increase in the viscosity of the fluoropolymer and/or the presence of a gel, such as taught in the Gel Content Method, disclosed herein.

[0028] The photoinitiators of the present disclosure are effective in causing cross-linking of the curable compositions of the present disclosure when exposed to actinic radiation. Such photoinitiators are known in the art and commercially available. Ideally, the photoinitiators are soluble or dispersable in the present composition (e.g., solvent) to ensure adequate reaction. Two classes of photoinitiator systems are disclosed herein. [0029] A first photoinitiator system comprises a single component, which when exposed to actinic radiation, cleaves forming two radicals. Such photoinitiators are known in the art. Exemplary photoinitiators of this type include: benzoin ethers (e.g., benzoin methyl ether or benzoin isopropyl ether) or substituted benzoin ethers (e.g., anisoin methyl ether). Other exemplary photoinitiators are substituted acetophenones such as 2,2-diethoxyacetophenone or 2,2- dimethoxy-2 -phenylacetophenone (commercially available under the trade designation “IRGACURE 651” from BASF Corp. (Florham Park, New Jersey) or under the trade designation “ESACURE KB-1” from Sartomer (Exton, Pennsylvania). Still other exemplary photoinitiators are substituted alpha-ketols such as 2-methyl-2 -hydroxypropiophenone, aromatic sulfonyl chlorides such as 2-naphthalenesulfonyl chloride, and photoactive oximes such as 1 -phenyl- 1,2- propanedione-2-(O-ethoxycarbonyl)oxime. Other suitable photoinitiators include, for example, 1- hydroxycyclohexyl phenyl ketone (commercially available under the trade designation “IRGACURE 184” from BASF Corp.), phenyl bis(2,4,6-trimethy1 benzoyl) phosphine oxide, diphenyl (2,4,6-trimethylbenzoyl) phosphme oxide, bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide (commercially available under the trade designation “IRGACURE 819” from BASF Corp.), 1 -[4-(2-hydroxyethoxy)phenyl] -2-hydroxy-2-methyl- 1 -propane- 1 -one (commercially available under the trade designation “IRGACURE 2959” from BASF Corp.), 2 -benzyl -2 -dimethylamino- 1- (4-morpholinophenyl)butanone (commercially available under the trade designation “IRGACURE 369” from BASF Corp.), 2-methyl-l-[4-(methylthio)phenyl]-2-morpholinopropan-l-one (commercially available under the trade designation “IRGACURE 907” from BASF Corp.), and 2- hydroxy-2 -methyl- 1 -phenyl propan- 1 -one (commercially available under the trade designation “DAROCUR 1173” from Ciba Specialty Chemicals Corp. (Tarrytown, New York).

[0030] The optimum amounts of the first photoinitiator system depend on the type used. Typical amounts include, but are not limited to, at least 0.01, 0.05, or even 0.1% wt; and at most 1, 3, or even 5 % wt versus the amount of amorphous fluoropolymer.

[0031] A second photoinitiator system is a multiple component system wherein a radical is generated through electron transfer to or from a second compound. For example, the photoinitiator system comprises a first component (A) which is a photosensitizer and a second component which comprises at least one of an iodonium salt (B) or an electron donor compound (C).

[0032] The first component (A) in the photoinitiator system is a photosensitizer compound. The photosensitizer is capable of electromagnetic radiation absorption somewhere within the range of the wavelength(s) of interest (for example if the actinic radiation is in the UV range, the photosensitizer should absorb wavelengths within the UV range). Suitable photosensitizers are believed to include compounds in the following categories: ketones, coumarin dyes (e.g., ketocoumarins), xanthene dyes, acridine dyes, thiazole dyes, thiazine dyes, oxazine dyes, azine dyes, aminoketone dyes, porphyrins, aromatic polycyclic hydrocarbons, p-substituted aminostyryl ketone compounds, aminotriaryl methanes, merocyanines, squarylium dyes and pyridinium dyes. Ketones (e.g., monoketones or alpha-diketones), ketocoumarins, aminoarylketones and p- substituted aminostyryl ketone compounds are preferred sensitizers. An exemplary photosensitizer includes 2-isopropylthioxanthone; 2-chlorothioxanthone (ITX); and 9,10-dibutoxyanthracene.

[0033] Suitable ketones include monoketones such as 2,2-, 4,4- or 2,4-dihydroxybenzophenone, di-2-pyridyl ketone, di-2-furanyl ketone, di-2 -thiophenyl ketone, benzoin, fluorenone, 2- chlorothioxanthone, acetophenone, benzophenone, and the like. Suitable diketones include aralkyldiketones such as anthraquinone, phenanthrenequinone, and the like. Suitable a-diketones include 2,3-butanedione, 2,3-pentanedione, 2,3 -hexanedione, 3,4-hexanedione, 2,3-heptanedione, 3,4-heptanedione, 2,3-octanedione, 4,5-octanedione, benzil, 2,2'- 3 3'- and 4,4'-dihydroxylbenzil, furil, di-3,3'-indolylethanedione, 2,3-bomanedione (camphorquinone), biacetyl, 1,2- cyclohexanedione, 1,2-naphthaquinone, acenaphthaquinone, and the like.

[0034] The second component can be (i) an iodonium salt, (ii) an electron donor compound, or (iii) an iodonium salt and an electron donor compound.

[0035] Suitable iodonium salts are described in U.S. Pat. Nos. 3,729,313, 3,741,769, 3,808,006, 4,250,053 and 4,394,403, the iodonium salt disclosures of which are incorporated herein by reference. The iodonium salt can be a simple salt (e.g., containing an anion such as Cl’, Bri, Tor C4H5SO3 ) or a metal complex salt (e.g., containing SbFsOH or AsFg ). Mixtures of iodonium salts can be used if desired.

[0036] Exemplary iodonium salts include bis(4-t-butylphenyl)iodonium hexafluoroantimonate (available under the trade designation “FP5034” from Hampford Research Inc., Stratford, CT), bis(4-t-butylphenyl) iodonium hexafluorophosphate (available under the trade designation “FP5035” from Hampford Research Inc.), (4-methoxyphenyl)phenyl iodonium triflate, bis(4-tert- butylphenyl) iodonium camphorsulfonate, bis(4-tert-butylphenyl) iodonium hexafluoroantimonate, bis(4-tert-butylphenyl) iodonium hexafluorophosphate, bis(4-tert-butylphenyl) iodonium tetraphenylborate, bis(4-tert-butylphenyl) iodonium tosylate, bis(4-tert-butylphenyl) iodonium triflate, ([4-(octyloxy)phenyl]phenyliodonium hexafluorophosphate), ([4- (octyloxy)phenyl]phenyliodonium hexafluoroantimonate), (4-isopropylphenyl)(4- methylphenyl)iodonium tetrakis(pentafluorophenyl) borate (available under the trade designation “RHODORSIL 2074” from Bluestar Silicones, East Brunswick, NJ), bis(4-methylphenyl) iodonium hexafluorophosphate (available under the trade designation “OMNICAT 440” from IGM Resins, St. Charles, IL), 4-(2-hydroxy-l-tetradecycloxy)phenyl]phenyl iodonium hexafluoroantimonate. Preferred iodonium salts include diaryliodonium salts such as (4- isopropylphenyl)(4-methylphenyl)iodonium tetrakis(pentafluorophenyl) borate, bis(4- methylphenyl) iodonium hexafluorophosphate, bis(4-t-butylphenyl)iodonium hexafluoroantimonate, and bis(4-t-butylphenyl) iodonium hexafluorophosphate.

[0037] Preferred electron donor compounds include amines (including aminoaldehydes and aminosilanes), ascorbic acid and its salts. The donor can be unsubstituted or substituted with one or more non-interfering substituents. Particularly preferred donors contain an electron donor atom such as a nitrogen, oxygen, phosphorus, or sulfur atom, and an abstractable hydrogen atom bonded to a carbon or silicon atom alpha to the electron donor atom.

[0038] Preferred amine donor compounds include alkyl-, aryl-, alkaryl- and aralkyl-amines such as triethanolamine, N,N'-dimethylethylenediamine, p-N N-dimethyl-aminophenethanol; aminoaldehydes such as p-N,N-dimethylaminobenzaldehyde, p-N,N-diethylaminobenzaldehyde, and 4-morpholinobenzaldehyde.

[0039] Suitable ether donor compounds include 4,4'-dimethoxybiphenyl, 1,2,4-trimethoxybenzene and 1,2,4,5-tetramethoxybenzene.

[0040] The photosensitizer and at least one of the iodonium salt or electron donor are present in "photochemically effective amounts", that is, amounts of each component are sufficient to enable at least partial crosslinking of the fluoropolymer upon exposure to the actinic radiation. Preferably, for every 100 parts of fluoropolymer, the curable composition of the present disclosure contains about 0.005 to about 10 parts (more preferably about 0.1 to about 4 parts) each of iodonium salt, sensitizer and donor. The amounts of each component are independently variable and thus need not be equal, with larger amounts generally providing faster cure, but shorter shelf life. Sensitizers with high extinction coefficients (e.g., above about 10,000) at the desired wavelength of irradiation for photopolymerization generally are used in reduced amounts. In one embodiment, at least 0.01, 0.05, or even 0.1% wt; and at most 1, 3, or even 5 % wt of the photosensitizer is used versus the amount of amorphous fluoropolymer; if the iodonium salt is used, at least 0.001, 0.01, 0.05, or even 0.1% wt; and at most 1, 3, or even 5 % wt of the iodonium salt is used versus the amount of the amorphous fluoropolymer; and if the electron donor is used, at least 0.001, 0.01, 0.05, or even 0.1% wt; and at most 1, 3, or even 5 % wt of the electron donor is used versus the amount of amorphous fluoropolymer.

[0041] A three component photoinitiator system comprising the photosensitizer, iodonium salt and an electron donor is described in U.S. Pat. No. 5,545,676 (Palazzotto, et al.), herein incorporated by reference with respect to the various components.

[0042] The photoinitiator/photosensitizer is activated by irradiation with actinic radiation. As used herein, actinic radiation refers to electromagnetic radiation in the ultraviolet, visible, and infrared wavelengths. [0043] Crosslinking agent

[0044] The curable fluoropolymer composition further comprises a crosslinking agent.

[0045] In one embodiment, the crosslinking agent is a multifunctional polyunsaturated compound, which includes allyl-containing cyanurates, isocyanurates, and phthalates, homopolymers of dienes, and co-polymers of dienes and vinyl aromatics. A wide variety of these crosslinking agents are commercially available including di- and triallyl compounds, divinyl benzene, vinyl toluene, vinyl pyridine, 1,2-cis-polybutadiene and their derivatives. Exemplary Type II coagents include a diallyl ether of glycerin, triallylphosphoric acid, diallyl adipate, diallylmelamine and triallyl isocyanurate (TAIC), tri(methyl)allyl isocyanurate (TMAIC), triallyl iscocyanurate, tri(methyl)allyl cyanurate, poly-triallyl isocyanurate (poly-TAIC), and xylylene-bis(diallyl isocyanurate) (XBD) N,N'-m-phenylene bismaleimide, diallyl phthalate, tris(diallylamine)-s- triazine, triallyl phosphite, 1,2-polybutadiene, ethyleneglycol diacrylate, diethyleneglycol diacrylate, or CH2=CH-Rfi-CH=CH2 wherein Rn is a perfluoroalkylene having from 1 to 8 carbon atoms.

[0046] The amount of crosslinking agent used generally will be at least 0.1, 0.5, or even 1 part by weight per 100 parts of amorphous fluoropolymer; and at most 2, 2.5, 3, or even 5 parts by weight per 100 parts of amorphous fluoropolymer.

[0047] Other Additives

[0048] In one embodiment, the compositions of the present disclosure comprise additional components, which facilitate the processing or final properties of the resulting article. For the purpose of, for example, enhancing the strength or imparting the functionality, conventional adjuvants, such as, for example, fillers, acid acceptors, process aids, or colorants may be added to the curable composition. Exemplary fillers include: an organic or inorganic filler such as clay, silica (SiC>2), alumina, iron red, talc, diatomaceous earth, barium sulfate, wollastonite (CaSiOfl. calcium carbonate (CaCCE), calcium fluoride, magnesium oxide, titanium oxide, iron oxide and carbon particles (such as graphite or carbon black, carbon fibers, and carbon nanotubes), silicon carbide, boron nitride, molybdenum sulfide, pigment, high temperature plastics, an electrically conductive filler, a heat-dissipating filler, and the like may be added as an optional additive to the composition. Those skilled in the art are capable of selecting specific fillers at required amounts to achieve desired physical characteristics in the vulcanized compound. The filler components may result in a compound that is capable of retaining a preferred elasticity and physical tensile, as indicated by an elongation and tensile strength value, while retaining desired properties such as retraction at lower temperature (TR-10). In one embodiment, the filler content is between 0.01 to 10 % or up to 30 % or even up to 50 % by weight based on the total weight of the composition.

[0049] Ionic Liquid [0050] The partially fluorinated amorphous polymers disclosed herein are dissolved and/or dispersed in the ionic liquid to form the curable compositions.

[0051] An ionic liquid is a unique salt, which is in a liquid state at about 100°C or less, has negligible vapor pressure, and high thermal stability. The ionic liquid is composed of a cation and an anion and has a melting point of generally about 100°C or less (i.e., being a liquid at about 100°C or less), about 95°C or less, or even about 80°C or less. Certain ionic liquids exist in a molten state even at ambient temperature since their melting points are less than room temperature, and therefore they are sometimes referred to as ambient temperature molten salts. The cation and/or anion of the ionic liquid are relatively sterically -bulky, and typically one and/or both of these ions are an organic ion. The ionic liquid can be synthesized by known methods, for example, by a process such as anion exchange or metathesis process, or via an acid-base or neutralization process.

[0052] The cation of the ionic liquid of the present disclosure may be an ammonium ion, a phosphonium ion, a sulfonium ion or the like, including various delocalized heteroaromatic cations, but is not limited thereto. The ammonium ion includes an ammonium ion selected from the group consisting of alkylammonium, imidazolium, pyridinium, pyrrolidinium, pyrrolinium, pyrazinium, pyrimidinium, triazonium, triazinium, quinolinium, isoquinolinium, indolinium, quinoxalinium, piperidinium, oxazolinium, thiazolinium, morpholinium, piperazinium, and a combination thereof. Examples of the phosphonium ion include a phosphonium ion selected from the group consisting of tetraalkylphosphonium, arylphosphonium, alkylarylphosphonium and a combination thereof. Examples of the sulfonium ion include a sulfonium ion selected from the group consisting of alkylsulfonium, arylsulfonium, thiophenium, tetrahydrothiophenium, and a combination thereof. The alkyl group directly bonded to nitrogen atom, phosphorus atom, or sulfur atom may be a linear, branched or cyclic alkyl group having a carbon number of at least 1, 2, or even 4 and not more than 8, 10, 12, 15, or even 20. The alkyl group may optionally contain heteroatoms such as O and N and S in the chain or at the end of the chain (e.g., a terminal -OH group). The aryl group directly bonded to nitrogen atom, phosphorus atom or sulfur atom may be a monocyclic or condensed cyclic aryl group having a carbon number of at least 5, 6, or even 8 and not more than 12, 15, or even 20. An arbitrary site in the structure constituting such a cation may be further substituted by an alkyl group, an alkenyl group, an alkynyl group, a cycloalkyl group, an aryl group, an aralkyl group, an arylalkyl group, an alkoxy group, an aryloxy group, a hydroxyl group, a carbonyl group, a carboxyl group, an ester group, an acyl group, an amino group, a dialkylamino group, an amide group, an imino group, an imide group, a nitro group, a nitrile group, a sulfide group, a sulfoxide group, a sulfone group, a halogen atom or the like, and a heteroatom such as oxygen atom, nitrogen atom, sulfur atom and silicon atom may be contained in the main chain or ring of the structure constituting the cation.

[0053] Specific examples of the cation include N-ethyl-N'-methylimidazolium, N-methyl-N- propylpiperidinium, N,N,N-trimethyl-N-propylammonium, N-methyl-N,N,N-tripropylammonium, N,N,N -trimethyl-N -butylammoniuim, N,N,N -trimethyl -N -methoxy ethylammonium, N -methyl - N,N,N-tris(methoxyethyl)ammonium, N,N-dimethyl-N-butyl-N-methoxyethylammonium, N,N- dimethyl-N,N -dibutylammonium, N -methyl -N,N -dibutyl-N -methoxy ethylammonium, N -methyl - N,N,N-tributylammonium, N,N,N-trimethyl-N-hexylammonium, N,N-diethyl-N-methyl-N-(2- methoxyethyl)ammonium, 1-propyl-tetrahydrothiophenium, 1-butyl-tetrahydrothiophenium, 1- pentyl-tetrahydrothiophenium, 1 -hexyl -tetrahydrothiophenium, glycidyltrimethylammonium, N- ethylacryloyl-N,N,N -trimethylammonium, N -ethyl-N -methylmorphonium, N,N,N- trioctylammonium, N-methyl-N,N,N-trioctylammonium, N,N-dimethyl-N-octyl-N-(2- hydroxyethyl)ammonium, and a combination thereof.

[0054] A cation not containing a functional group or moiety exhibiting reactivity (for example, an unsaturated bond having reaction activity) is advantageous in view of heat resistance, and examples of such a cation include N-methyl-N-propyl piperidinium and N,N,N-trimethyl-N- propylammonium .

[0055] The anion of the ionic liquid of the present disclosure may be, for example, a sulfate (R- OSO3 ), a sulfonate (R-SO3 ), a carboxylate (R-CO2 ), a phosphate ((RO)2P(=O)O ), a borate represented by the formula: BR ₄ . such as tetrafluoroborate (BF ₄ ) and tetraalkylborate, a phosphate represented by the formula: PRf, such as hexafluorophosphate (PFg ) and hexaalkylphosphate, an imide (R2N ), a methide (R3C ), nitrate ion (NO3 ), or nitrite ion (NO2 ). In the formula, each R may be independently a hydrogen atom, a halogen atom (fluorine, chlorine, bromine, iodine), a substituted or unsubstituted alkyl, alkenyl, alkynyl, cycloalkyl, aryl, aralkyl, arylalkyl, acyl or sulfonyl group, or the like. A heteroatom such as an oxygen atom, a nitrogen atom and a sulfur atom may be contained in the main chain or ring of the group R, and a part or all of hydrogen atoms on the carbon atom of the group R may be replaced with fluorine atoms. In the case where a plurality of R's are present in the anion, these R's may be the same or different. Because of good compatibility with fluoropolymer in general, it is advantageous that a part or all of hydrogen atoms on the carbon atom of the group R in the anion be replaced by fluorine atoms and it is advantageous that the anion contains a perfluoroalkyl group.

[0056] Examples of the anion containing a perfluoroalkyl group, which can be advantageously used, include a bis(perfluoroalkylsulfonyl)imide ((RfSCE N ), a perfluoroalkylsulfonate (RfSO , ) and a tris(perfluoroalkylsulfonyl)methide ((RfSCE^C ) (wherein Rf represents a perfluoroalkyl group). The carbon number of the perfluoroalkyl group may be, for example, from at least 1, 2, 3 or even 4 to at most 8, 10, 12, 15, or even 20. Specific examples of the bis(perfluoroalkylsulfonyl)imide include: bis(trifluoromethanesulfonyl)imide, bis(pentafluoroethanesulfonyl)imide, bis(heptafluoropropanesulfonyl)imide and bis(nonafluorobutanesulfonyl)imide. Specific examples of the perfluoroalkylsulfonate include: trifluoromethane sulfonate, pentafluoroethanesulfonate, heptafluoropropane sulfonate and nonafluorobutanesulfonate. Specific examples of the tris(perfluoroalkylsulfonyl)methide include: tris(trifluoromethanesulfonyl)methide, tris(pentafluoroethanesulfonyl)methide, tris(heptafluoropropanesulfonyl)methide, tris(nonafluorobutanesulfonyl)methide, and a combination thereof.

[0057] As for the ionic liquid composed of the above-described cation and anion, N-methyl-N- propylpiperidinium bis(trifluoromethanesulfonyl)imide, N-methyl-N-propylpiperidinium bis(trifluoromethanesulfonyl)imide, N-ethyl-N'-methylimidazolium bis(trifluoromethanesulfonyl)imide, N,N,N-trimethyl-N-hexylammonium bis(trifluoromethanesulfonyl)imide and N-methyl-N,N,N-tributylammonium bis(trifluoromethanesulfonyl)imide can be advantageously used, because of excellent heat resistance and good compatibility with fluoropolymer. In the usage requiring non-coloration, N- methyl-N-propylpiperidinium bis(trifluoromethanesulfonyl)imide, N,N,N-trimethyl-N- hexylammonium bis(trifluoromethanesulfonyl)imide and N-methyl-N,N,N-tributylammonium bis(trifluoromethanesulfonylimide, which are free of an aromatic ring, are particularly suitable. [0058] In one embodiment, the coatable composition comprises at least 10, 20, 30 or even 40 wt % of the ionic liquid. In one embodiment, the coatable composition comprises at most 50, 60, 70, 80, 90, or even 99 wt % of the ionic liquid.

[0059] In one embodiment, the amorphous fluoropolymer content of the curable compositions is preferably as high as possible, for example, at concentrations from at least 50, 75, 80, 85, or even 90 % by weight; and at most 95, 98, 99, or even 99.5 % by weight based on the total weight of the curable composition.

[0060] The partially fluorinated amorphous polymers dissolved and/or dispersed in the liquid solvent are coatable. In one embodiment, the compositions have a viscosity at 25 °C of at least 50, 100, 500, 1000, 2000, 4000, 6000 or even 10000 cP (centiPoise). In one embodiment, the compositions have a viscosity at 25°C of at most 2000, 4000, 6000, 8000, 10000, 15000, 20000, 50000, 100000, 200000, 500000, or even 1000000 cP. The low viscosities can enable the coating compositions to be dispensable.

[0061] In another embodiment, the coatable compositions have a viscosity at 100°C of at least 1, 2, 5, 10, 50, or even 100 Pascals’s; and at most 500, 1000, 2000, 3000, 4000 or even 5000 Pascals. Techniques such as parallel plate rheometer or rubber process analyzer can be used to determine the viscosity. Additional liquid solvents may be present in the curable fluoropolymer composition, typically as a result of carriers or impurities in the components. Ideally, these additional liquid solvents are kept to a minimum. In one embodiment, the liquid solvent consists essentially of the ionic liquid, meaning that the inert liquid present in the curable fluoropolymer composition comprises at least 90, 95, 98, 99, or even 99.9 wt % of the ionic liquid. In some embodiments, no additional liquid is present other than the ionic liquid.

[0062] Advantageously, the ionic liquid is used as a liquid solvent to at least partially dissolve the partially fluoropolymer. Ionic liquid is unique because it is able to at least partially solubilize the partially fluorinated amorphous polymer and has a good environmental profile and is nonflammable making it especially useful.

[0063] In one embodiment, the ionic liquid and/or the curable fluoropolymer composition of the present disclosure has a low environmental impact. In this regard, the ionic liquid and/or the curable fluoropolymer composition of the present disclosure may have a global warming potential (GWP) of less than 10, 5, 2, or 1. As used herein, GWP is a relative measure of the global warming potential of a compound based on the structure of the compound. See paragraphs [0020]- [0022] of U.S. Publ. No. 2015/0083979 (Costello et al.) for discussion on how to determine the GWP.

[0064] In one embodiment, the ionic liquid and/or the curable fluoropolymer composition of the present disclosure have an atmospheric lifetime of less than 10 years, or even less than 5 years when tested as disclosed in paragraph [0060] of U.S. Publ. No. 2020/0002589 (Uamanna).

[0065] Non-flammability can be assessed by using standard methods such as ASTM D-3278-96 e-l“Standard Test Method for Flash Point of Uiquids by Small Scale Closed-Cup Apparatus”. In one embodiment, the ionic liquid and/or the curable fluoropolymer composition of the present disclosure is non-flammable based on closed-cup flashpoint testing following ASTM D-3278-96 e- 1.

[0066] Method of making

[0067] The curable composition comprising the partially fluorinated amorphous polymer, the photoinitiator, crosslinking agent, ionic liquid, and optional additives can be combined together, using techniques known in the art, and photochemically cured.

[0068] In one embodiment, the curable composition is coated onto a substrate and then exposed to either thermal radiation or actinic radiation. For example, the curable composition is coated onto a substrate using techniques known in the art including, for example, dip coating, spray coating, spin coating, blade or knife coating, bar coating, roll coating, and pour coating (i.e., pouring a liquid onto a surface and allowing the liquid to flow over the surface)). Substrates may include, metals (such as carbon steel, stainless steel, and aluminum), plastics (such as polyethylene, or polyethylene teraphthalate), or release liners, which are a temporary support comprising a backing layer coated with a release agent (such as a silicone, fluoropolymer, or polyutherane). The composite comprising the substrate and a layer of curable composition is then exposed to thermal or actinic radiation to at least partially cure the curable composition. In one embodiment, a thin coating of the curable composition is disposed on a substrate, for example a coating thickness of at least 10 nm or even 100 nm to at most 1 pm, 10 pm, or even 100 pm.

[0069] In one embodiment, the coating composition comprising the amorphous partially fluorinated polymer and the ionic liquid is heated to decrease the viscosity to enable easier coating and/or dispensing of the coating composition. Exemplary temperatures include at least 50, 80, or even 100°C; and at most 250, 200, 150, or even 120°C, depending on the temperature limitations of the equipment and/or decomposition temperature of the amorphous fluoropolymer.

[0070] In one embodiment, the thin coating is substantially crosslinked, meaning that when tested following the Gel Content Measurement described below, there is at least 65, 70, 80, or even 90% gelling.

[0071] In one embodiment, the curable composition is at least partially cured using actinic radiation. In one embodiment, the curable composition is exposed to wavelengths from at least 180, 200, 210, 220, 240, 260, or even 280 nm; and at most 700, 800, 1000, 1200, or even 1500 nm. In one embodiment, the curable composition is exposed to wavelengths from at least 180, 210, or even 220 nm; and at most 340, 360, 380, 400, 410, 450, or even 500 nm. In one embodiment, the curable composition is exposed to wavelengths from at least 400, 420, or even 450 nm; and at most 700, 750, or even 800 nm. In one embodiment, the curable composition is exposed to wavelengths from at least 800, 850, or even 900 nm; and at most 1000, 1200, or even 1500 nm.

[0072] Any light source, as long as part of the emitted light can be absorbed by the photo-initiator or photo-initiator system, may be employed as a radiation source, such as, a high or low pressure mercury lamp, a cold cathode tube, a black light, a light emitting diode, a laser, and a flash light. Of these, the preferred source is one exhibiting a relatively long wavelength UV-contribution having a dominant wavelength of 300-400 nm. UV radiation is generally classed as UV-A, UV-B, and UV-C as follows: UV-A: 400 nm to 320 nm; UV-B: 320 nm to 290 nm; and UV-C: 290 nm to 100 nm.

[0073] In one embodiment, the dosage of the actinic radiation is 10-1000 watts.

[0074] In one embodiment, the coating compositions can be processed in a continuous fashion. In this type of processing, the coating composition is coated onto a web, and then transported to a curing station containing the radiation (thermal or electromagnetic) source. The cured fluoroelastomer composition can then be transported to a cutting station, whereby articles of desired shapes are cut from the web of fluoroelastomer. Such a process can enable faster processing of articles, due to the continuous nature of the processing. The low flammability and/or good environmental profde of the ionic liquid enables the coating compositions to be continuously processed without the necessity of making equipment explosion proof.

[0075] In another embodiment, the coating composition is coated directly onto the article and cured in place. For example, if a gasket for a part (e.g., a head) is needed, the coating composition could be coated directly onto the part and then cured. Such a process would enable made-to-order parts and eliminates cutting and/or the need for a mold.

[0076] The articles of the present disclosure are shaped and can include gaskets, ring lip seals, washer seals, O-rings, grooved seals, etc.

EXAMPLES

[0077] All materials are commercially available, for example from Sigma- Aldrich Chemical Company, Milwaukee, WI, USA, or known to those skilled in the art, unless otherwise stated or apparent.

[0078] The following abbreviations are used in this section: m=meters, cm=centimeters, pm=micrometers, wt %= percent by weight, min=minutes, mJ=milliJoule, mV= millivolt, MPa= megapascal, °C=degrees Celsius. Abbreviations for materials used in this section, as well as descriptions of the materials, are provided in Table 1.

Table 1

[0079] Characterization Methods

[0080] Gel content test

[0081] Sample (dispensed sample or sheet) was soaked in acetone for 1 min. Then sample was rinsed 5 times by Acetone. Sample was dried in an oven under 80 °C for 10 min.

[0082] Gel content % was calculated by Weight after drying

Gel contents % = - x 100

Initial weight

[0083] Comparative Examples 1 through 3 and Examples 1 and 4

[0084] A planetary mixer was used for mixing of the ingredients for CE-1 to CE-3 and EX-1 and EX-4 as listed in Tables 3 and 4. After mixing, the samples were dispensed using a dispenser available under the trade designation SHOT MINI 200SX from MUSASHI ENGINEERING, INC, using a 20 gauge (0.61 mm inner diameter) nozzle at 100°C. Dispensed material was formed into sheets of about 1 mm thickness.

[0085] Comparative Example 4 and Examples 2 and 3

[0086] An open roll mill with 6 inch (15.24 cm) diameter rolls was used for mixing of the ingredients of CE-4 and EX-2 and EX-3 as listed in Table 4. For these samples, a small amount of material was pressed (Pressure: 5MPa, temperature: 100 °C) for 1 minute to form a 200 micrometer thick sample.

[0087] All of the samples (EX-1 to EX-4 and CE-1 to CE-4) were cured in a UV irradiator available under the trade designation MODEL DRS from Heraeus Noblelight America LLC, Buford, GA, using the following conditions: bulb type: H, line Speed: 13.4 m/min, pass number: 10 times. The UV energy of the system is provided in Table 2. The gel content for each sample, without UV irradiation and with UV irradiation, are shown in Tables 3 and 4.

Table 2. UV energy

Table 3.

Table 4. [0088] Foreseeable modifications and alterations of this invention will be apparent to those skilled in the art without departing from the scope and spirit of this invention. This invention should not be restricted to the embodiments that are set forth in this application for illustrative purposes. To the extent that there is any conflict or discrepancy between this specification as written and the disclosure in any document mentioned or incorporated by reference herein, this specification as written will prevail.